The present invention relates to a fixed-amount-of-liquid ejecting method and apparatus which are suitably used for ejecting a liquid in fixed amount, the liquid including a viscous fluid, a material having consistency, etc. More particularly, in the field of ejecting or applying a very small amount of liquid, the present invention relates to a technique for controlling the operation of ejecting or applying a very small amount of liquid in a high-speed and precise manner. Further, the present invention relates to a technique for filling a liquid in a liquid reservoir for use in all kinds of processes, e.g., an electronic parts manufacturing process and an electronic parts assembling process, which require a step of ejecting or applying a liquid that includes a viscous fluid and a material having consistency.
Generally, a fixed-amount-of-liquid ejecting apparatus is employed for the purpose of ejecting a desired amount of liquid, and a method of utilizing both the fixed-amount-of-liquid ejecting apparatus and a robot capable of moving a member to which a liquid is to be applied (referred to also as an applied member hereinafter) or a nozzle is employed for the purpose of applying the liquid in a desired pattern.
As techniques for ejecting a liquid, there are known a pneumatic type method and a plunger type method. In the pneumatic type method, compressed air regulated in pressure is imparted to a liquid for a desired period of time. In the plunger type method, a push member operatively connected to a driving source is disposed in a liquid-tight condition, and it is moved through a desired distance.
The pneumatic type method is a quite simple method utilizing compressed air. Since only compressed air contacts a liquid except for a reservoir, this provides such an advantage that the liquid can be employed while it is kept clean. For this reason, the pneumatic type method is very popularly practiced.
On the other hand, the plunger type method is advantageous in that the volume of liquid ejected can be determined based on a cross-sectional area of the push member contacting the liquid and a distance through which the push member is moved. For this reason, the plunger type method is a method utilized when applying a very small amount of liquid as required in operation of filling or pipetting the liquid.
Conventionally, a liquid has been applied in a desired pattern as follows. A liquid in a reservoir is forced to move using one of the above-described methods, causing the liquid to be ejected through a nozzle end serving as an apparatus ejection orifice. Simultaneously, one or both of the apparatus ejection orifice and a member to which a liquid is to be applied are moved relatively to each other so that the liquid draws the desired pattern. However, because the above-described methods require a time until a flow speed of the liquid reaches a certain constant value, it has been very difficult to draw a uniform line of the applied liquid for a time until the constant flow speed is obtained. Such an adverse effect is significant particularly in the case of employing a highly viscous liquid or applying a liquid at a high speed. Concretely, the adverse effect appears in the form of narrowing or discontinuity in a starting portion of the applied liquid line, and in the form of fatting or pooling in an ending portion of the applied liquid line.
Japanese Unexamined Patent Publication No. 4-49108, for example, discloses one example of a conventional fixed-amount-of-liquid ejecting apparatus for use in regularly or irregularly coating an electronic material on a board in the form of points and lines in semiconductor manufacturing processes. In the disclosed ejecting apparatus, the amount of liquid ejected through an ejection orifice is controlled in accordance with such a parameter as the speed and cycle time of rotation of a screw, etc. With the disclosed apparatus, the rotational speed and the stop timing of the screw are controlled with high accuracy. Therefore, the amount of the ejected liquid is stabilized and the liquid ejection in fixed amount can be achieved even in a continuous ejection mode without being affected by the viscosity and fluidity of the liquid and the amount of liquid present in a reservoir. In the above prior art apparatus, however, the liquid is ejected and stopped respectively upon rotation and stoppage of the screw, and the ejection orifice is left in a physically open state during the time in which the ejection is stopped. This has raised the following problem, particularly in the case of the liquid having a low viscosity or the case of pressurizing the liquid in the reservoir. If there is a relatively large clearance between an outer peripheral surface of the screw and an inner peripheral surface of a screw housing, the liquid is not positively shut off at the time of stopping the liquid ejection, and the liquid tends to leak due to the own weight and a force applied to pressurize the liquid. On the other hand, if the clearance between the outer peripheral surface of the screw and the inner peripheral surface of the screw housing is set to such a small value as able to overcome the above problem, another problem has arisen in that fillers, for example, mixed in the electronic material are broken.
Further, the pneumatic type method employed a highly compressible air, and therefore has a big difficulty in achieving a desired pressure in a short time. Stated otherwise, it has been more difficult to form the applied liquid line having the same shape between start and end points and an intermediate area with the pneumatic type method. Another problem has been encountered in that because the liquid viscosity changes depending on, e.g., variations in an ambient atmosphere and a chemical reaction of the liquid itself, the amount of the ejected liquid is also changed depending on a change of the liquid viscosity when the pneumatic type method is employed in which a regulated constant pneumatic pressure acts upon the liquid. Thus, it has been impossible to apply a liquid tending to change its viscosity in the fine uniform form by using a pneumatic type ejecting apparatus.
The plunger type method has a basic function in ejecting a liquid in predetermined volume, and therefore it has been primarily used in applications for precisely pipetting or filling a desired amount of liquid. Also, the plunger type method has features superior in preciseness and constant amount because the amount of the ejected liquid is determined by a distance through which a piston moves. For that reason, the ejection operation is generally performed in a very cautious and slow manner. Thus, in the technique using the plunger type method, the essential purport resides in precisely ejecting and applying a fixed amount of liquid, and even if a change occurs in flow speed of the liquid during the ejection, there is no problem so long as the resulting amount of the applied liquid is uniform. Further, the plunger type method is avoided from being used for ejecting a highly viscous liquid. The reason is that a highly viscous liquid requires a very great force to be acted on the liquid for producing a flow of the same. Such a great force causes expansion and distortion of the reservoir and the piston, as well as compression of a liquid which hardly develops elastic deformation. These deformations impair the features of the plunger type method, i.e., preciseness and constant amount.
Particularly, when applying a highly viscous liquid at a high speed, or when using a narrow or long nozzle even in the case of applying a low viscous liquid, a very high pressure requires to be acted upon the liquid, and deformations such as expansion, distortion and compression become more remarkable. Further, because of such a specific feature of the plunger type method that only an ejection orifice is opened to the atmosphere, an adverse effect of those deformations is increased as a higher pressure is acted upon the liquid and as the ejection orifice has a smaller diameter. Concretely, the adverse effect has appeared in such phenomena as a delay and a liquid dripping in the ejection process, and discontinuity, pooling and distortion in the form of the applied liquid line. Although the above-mentioned deformations are very small, the adverse effect caused by those deformations brings about a fatal problem in the case of applying a liquid in the fine form, or the case of applying a liquid in very small amount, or the case of applying a liquid at a high speed. For that reason, the plunger type method is quite unsuitable for any of those cases requiring a high pressure.
Further, it is generally known that for the purpose of ejecting a desired amount of liquid, a fixed-amount-of-liquid ejecting apparatus is employed which ejects a fixed amount of liquid supplied from a liquid reservoir through an ejection valve, and that for the purpose of applying a liquid in a desired pattern, a method of utilizing both the fixed-amount-of-liquid ejecting apparatus and a robot capable of moving a member to which a liquid is to be applied or a nozzle is employed. Where a liquid having a medium or higher level of viscosity, for example, is filled in a liquid reservoir, particularly a syringe, it is often practiced to provide a liquid outlet on a pressure container in which the liquid is filled beforehand, to air-tightly connect the liquid reservoir, particularly the syringe, to the liquid outlet, and to introduce air to the pressure container for pressurization, thereby causing the liquid to be filled into the syringe through the liquid outlet.
The above prior art however has a serious problem as follows. When pressurized air is introduced to the pressure container for filling the liquid into the syringe through the liquid outlet and a syringe connecting portion, the liquid is released to the atmosphere in the syringe. For a liquid having higher viscosity, therefore, the liquid tends to be released more vigorously and to fill the syringe while entrapping a larger amount of bubbles corresponding to an inner diameter of the syringe connecting portion. The reason is that since the syringe into which the liquid is filled is under an atmospheric condition, the filled liquid is brought into a free state in the syringe connecting portion.
An object of the present invention is to provide a fixed-amount-of-liquid ejecting method and apparatus which are suitably used for ejecting a liquid in fixed amount, the liquid including a viscous fluid, a material having consistency, etc.
Another object of the present invention is to provide a method and apparatus with which, when ejecting or applying a very small amount of liquid, the liquid can be applied in a desired form at a high speed and precisely without depending on viscosity of the liquid. Still another object of the present invention is to provide a method and apparatus with which, particularly even when employing a highly viscous liquid or applying a liquid at a high speed, a shape of the applied liquid line can be very easily controlled in starting and ending portions of the applied liquid line. For example, when the liquid should be applied in a linear uniform shape, the applied liquid line can be formed with a uniform width from the start point to the end point of the line without narrowing and fatting.
Still another object of the present invention is to provide a liquid ejecting method and apparatus which can more positively shut off a liquid at the time of stopping the liquid ejection without a risk of breaking fillers, and can securely avoid a leakage of the liquid.
Still another object of the present invention is to provide a liquid ejecting or applying method and apparatus which enables an applied liquid to be drawn in a uniform line without taking a time until a flow speed of the liquid reaches a certain value.
Still another object of the present invention is to provide a fixed-amount-of-liquid ejecting method and apparatus with which, when filling a liquid in a liquid reservoir, particularly in a syringe, the liquid can be filled without entrapping bubbles, preferably, in a fully automated manner.
The present invention provides a fixed-amount-of-liquid ejecting method for ejecting a liquid in fixed amount from a liquid reservoir through an ejection valve, the method being featured by comprising a step of applying a pressure to the liquid beforehand prior to starting ejection of the liquid and/or holding a pressure near an ejection orifice after the end of the liquid ejection at a predetermined specific value using a push member disposed to push a liquid stored in the liquid reservoir so that an ejection rate of the liquid through the ejection orifice is kept constant.
The predetermined specific value is preferably maintained by detecting a liquid pressure near the ejection orifice and automatically regulating an ejection pressure of the liquid in accordance with a detected result.
The above fixed-amount-of liquid ejecting method according to the present invention is further featured by a step of controlling a pressure of the liquid supplied from the liquid reservoir to the ejection valve. The control of the liquid pressure is preferably performed by controlling a pressure of the liquid stored in the liquid reservoir, preferably by controlling, preferably constant or variable, a rate at which the liquid stored in the liquid reservoir reduces.
The above fixed-amount-of-liquid ejecting method according to the present invention is further featured by that a temperature of the liquid in the liquid reservoir and the ejection valve is controlled to be held at a desired temperature.
The above fixed-amount-of-liquid ejecting method according to the present invention is further featured by that the ejection valve includes a nozzle having in itself a function of a needle valve.
Stated otherwise, in the concrete form of the fixed-amount-of-liquid ejecting method according to the present invention, the step of applying a pressure to the liquid beforehand prior to starting ejection of the liquid and/or holding a pressure near an ejection orifice after the end of liquid ejection at a predetermined specific value, so that an ejection rate of the liquid through the ejection orifice is kept constant, is preferably realized as follows. For ejecting the liquid in fixed amount from the liquid reservoir through the ejection valve, the above step comprises a step of detecting a liquid pressure near the ejection orifice and automatically regulating an ejection pressure of the liquid in accordance with a detected result; and/or a step of controlling a pressure of the liquid stored in the liquid reservoir by, preferably, controlling, preferably constant or variable, a rate at which the liquid stored in the liquid reservoir reduces; and/or a step of controlling a pressure of the liquid supplied from the liquid reservoir to the ejection valve. Further, a temperature of the liquid in the liquid reservoir and the ejection valve is controlled to be held at a desired temperature. Still further, the ejection valve includes a nozzle having in itself a function of a needle valve.
The present invention also provides a fixed-amount-of-liquid ejecting method which is featured by further including a liquid filling process wherein, when filling a liquid in the liquid reservoir from a pressure container in which the liquid is stored beforehand, a liquid pressure in the liquid reservoir is controlled to a constant pressure lower than the pressure of air introduced to the pressure container for pressurization, thereby automatically filling the liquid without entrapment of bubbles.
The above liquid filling process is further featured by automatically stopping filling of the liquid is upon sensing of a full-amount state of the liquid in the liquid reservoir. Also, the above liquid filling process is further featured by automatically stopping filling of the liquid upon sensing of a small remaining-amount state of the liquid in the pressure container. Moreover, the above liquid filling process is further featured by removing bubbles accidentally generated in the liquid reservoir.
Stated otherwise, in the concrete form of the liquid filling process, when filling a liquid in the liquid reservoir from a pressure container in which the liquid is stored beforehand, a liquid pressure in the liquid reservoir is controlled to a constant pressure lower than the pressure of air introduced to the pressure container for pressurization; and/or bubbles accidentally generated in the liquid reservoir are removed; and/or filling of the liquid is automatically stopped upon sensing of a full-amount state of the liquid in the liquid reservoir or of a small remaining-amount state of the liquid in the pressure container, as necessary, thereby automatically filling the liquid without entrapment of bubbles.
Furthermore, the present invention provides a fixed-amount-of-liquid ejecting apparatus comprising a liquid reservoir, means for pressurizing a liquid comprising a push member disposed to push a liquid in the liquid reservoir, and an ejection valve communicating with the liquid reservoir, thereby ejecting the liquid in fixed amount from the liquid reservoir through the ejection valve, wherein the apparatus further comprises operation control means for controlling operations of the pressurizing means and the ejection valve, and ejection pressure control means for automatically regulating an ejection pressure of the liquid.
Preferably, the ejection pressure control means comprises an input/output unit, a processing unit and a storage unit, and functions to automatically regulate an ejection pressure of the liquid in accordance with a detected result of a pressure sensor for detecting a liquid pressure near an ejection orifice. The ejection valve preferably includes means for mechanically opening and closing an ejection orifice of the ejection valve. Preferably, the pressurizing means comprises means for pressurizing the liquid stored in the liquid reservoir under a pressure depending on viscosity of the liquid. Also, the pressurizing means preferably comprises a push member disposed to push the liquid stored in the liquid reservoir in a precise and fluid-tight manner, more preferably comprises a push member which is associated with an air cylinder for pressing the push member and having a bore diameter sufficiently greater than the inner diameter of the liquid reservoir, and which is disposed to push the liquid stored in the liquid reservoir in a precise and fluid-tight manner. Preferably, the operation control means comprises a pressure sensor for detecting a liquid pressure near an ejection orifice, and means for operating the pressurizing means in accordance with a signal from the pressure sensor.
As another feature, the fixed-amount-of-liquid ejecting apparatus according to the present invention further comprises liquid temperature control means for controlling a liquid temperature.
Stated otherwise, in the concrete form of the fixed-amount-of-liquid ejecting apparatus according to the present invention, the apparatus comprises a liquid reservoir; means for pressurizing a liquid in the liquid reservoir, preferably means for pressurizing the liquid stored in the liquid reservoir under a pressure depending on viscosity of the liquid, more preferably a push member disposed to push the liquid stored in the liquid reservoir in a precise and fluid-tight manner, most preferably a push member which is associated with an air cylinder for pressing the push member and having a bore diameter sufficiently greater than the inner diameter of the liquid reservoir; and an ejection valve communicating with the liquid reservoir and mechanically opening and closing the ejection orifice of the ejection valve. The apparatus further comprises operation control means for controlling operations of the pressurizing means and the ejection valve, the operation control means preferably comprising a pressure sensor for detecting a liquid pressure near an ejection orifice and means for operating the pressurizing means in accordance with a signal from the pressure sensor; and ejection pressure control means for automatically regulating an ejection pressure of the liquid, the ejection pressure control means preferably comprising an input/output unit, a processing unit and a storage unit, and functioning to automatically regulate an ejection pressure of the liquid in accordance with a detected result of a pressure sensor for detecting a liquid pressure near an ejection orifice; and/or liquid temperature control means for controlling a liquid temperature.
As still another feature, in above the fixed-amount-of-liquid ejecting apparatus according the present invention, the ejection valve includes a nozzle provided with a valve mechanism in a nozzle body.
As still another feature, in the above fixed-amount-of-liquid ejecting apparatus according to the present invention, the ejection valve comprises a valve body having an inlet port in communication with the liquid reservoir, a liquid chamber formed therein to contain the liquid introduced through the inlet port, and an outlet port through which the liquid in the liquid chamber is ejected; a needle-like valve stem disposed in the liquid chamber movably between a first position and a second position; a valve seat formed to receive a tip of the valve stem to thereby close the outlet port when the valve stem is in the first position; and pressure compensating means for changing the volume of the liquid chamber in synch with movement of the valve stem so that variations of liquid pressure in the liquid chamber caused by movement of the valve stem is canceled.
As still another feature, the fixed-amount-of-liquid ejecting apparatus according the present invention further includes a filling apparatus which comprises a liquid reservoir including a plunger inserted therein in an airtight manner, a pressure container in which the liquid is stored beforehand, and a plunger direct-actuating control mechanism for maintaining a liquid pressure in the liquid reservoir at a constant pressure lower than the pressure of air introduced to the pressure container for pressurization, thereby automatically filling the liquid in the liquid reservoir without entrapment of bubbles.
The above filling apparatus is further featured by comprising means for sensing a full-amount state of the liquid in the liquid reservoir and/or means for sensing a small remaining-amount state of the liquid in the pressure container, and for automatically stopping filling of the liquid in accordance with a sensed signal. The above filling apparatus is further featured by including a valve structure which has an air release hole for communicating the plunger inserted in the liquid reservoir with the outside and is able to close the air release hole at any time, so that bubbles accidentally generated in the liquid reservoir may be removed.
Stated otherwise, in the concrete form of the liquid filling apparatus, the apparatus comprises a liquid reservoir including a plunger inserted therein in an airtight manner; a pressure container in which the liquid is stored beforehand; and a plunger direct-actuating control mechanism for maintaining a liquid pressure in the liquid reservoir at a constant pressure lower than the pressure of air introduced to the pressure container for pressurization; and/or means for sensing a full-amount state of the liquid in the liquid reservoir and/or means for sensing a small remaining-amount state of the liquid in the pressure container, and for automatically stopping filling of the liquid in accordance with a sensed signal as necessary; and/or a valve structure which has an air release hole for communicating the plunger inserted in the liquid reservoir with the outside and is able to close the air release hole at any time, so that bubbles accidentally generated in the liquid reservoir may be removed, thereby automatically filling the liquid in the liquid reservoir without entrapment of bubbles.
The mode for carrying out the present invention will be described below in connection with the form including liquid temperature control means. As described above, the present invention resides in a fixed-amount-of-liquid ejecting method wherein, for ejecting a liquid in fixed amount from a liquid reservoir through an ejection valve, the method comprises a step of applying a pressure to the liquid beforehand prior to starting ejection of the liquid and/or holding a pressure near an ejection orifice after the end of liquid ejection at a predetermined specific value so that an ejection rate of the liquid through the ejection orifice is kept constant. The control of the liquid pressure in the above method is performed by controlling a pressure of the liquid stored in the liquid reservoir, preferably by controlling constant or variable a rate at which the liquid stored in the liquid reservoir reduces. Also, temperatures of the liquid in the liquid reservoir and the ejection valve are controlled to be held at desired temperatures.
Further, the apparatus of the present invention includes operation control means for controlling operations of the pressurizing means and the ejection valve, and liquid temperature control means for controlling a liquid temperature. The apparatus of the present invention may be of the pneumatic type or the plunger type. The following description will be made of features of the pneumatic type apparatus or features common to both the types of apparatus unless otherwise specified.
The ejection valve includes means for mechanically opening and closing the ejection orifice of the ejection valve. The pressurizing means is means for pressurizing the liquid stored in the liquid reservoir under a pressure depending on viscosity of the liquid. Preferably, the pressurizing means is a push member disposed to push the liquid stored in the liquid reservoir in a precise and fluid-tight manner. The push member is associated with an air cylinder for pressing the push member and having a bore diameter sufficiently greater than the inner diameter of the liquid reservoir. The operation control means comprises a pressure sensor for detecting a liquid pressure near the ejection orifice, and means for operating the pressurizing means in accordance with a signal from the pressure sensor. The liquid temperature control means comprises temperature sensors for detecting respective liquid temperatures in the liquid reservoir and the pressure container, and heating/cooling units maintained at desired temperatures in accordance with signals from the temperature sensors.
The liquid temperature control means will now be described.
Viscosity of a liquid changes depending on not only variations in temperature but also a chemical reaction of the liquid itself, for example. The amount of ejected liquid is also slightly changed depending on such a change of the liquid viscosity. In the prior art, however, an attention has been focused on precise control of the rotational speed of a screw and the timing of stopping the screw, and no considerations have been paid to viscosity and fluidity of a liquid as well as the amount of liquid in a liquid reservoir. The inventors have conducted a number of experiments based on such a hypothesis that controlling a liquid temperature so as to inhibit its change is effective in suppressing one, more exactly, primary one of factors which cause a viscosity change. As a result, it has been proved that controlling a liquid temperature to be held constant is effective in ejecting a liquid in fixed amount.
From an aspect of method, control of a liquid temperature is carried out by controlling temperatures of the liquid in the liquid reservoir and the ejection valve to be held at desired temperatures. From an aspect of apparatus, the liquid temperature control means is provided which comprises temperature sensors for detecting respective liquid temperatures in the liquid reservoir and the pressure container, and heating/cooling units maintained at desired temperatures in accordance with signals from the temperature sensors.
A description will now be made of other features of the present invention, i.e., the step of applying a pressure to the liquid beforehand prior to starting ejection of the liquid and/or holding a pressure near an ejection orifice after the end of liquid ejection at a predetermined specific value, and means for mechanically opening and closing the ejection orifice in an aspect of apparatus.
For example, when ejecting the liquid in relatively small fixed amount, the pressure in a flow passage after the end of the ejection, particularly the pressure near the ejection orifice, is controlled to be kept at the predetermined specific value, whereby the subsequent ejection of the liquid can be always performed under the constant flow passage condition. Accordingly, by properly setting the force, time, etc. for pressurizing the liquid in the liquid reservoir, the ejection of the liquid in an amount corresponding to the set values can be repeatedly reproduced with high reliability. On the other hand, when ejecting the liquid in relatively large fixed amount, in addition to the above control, the pressure of the supplied liquid is controlled also during the liquid ejection based on the detected result of the liquid pressure in such a manner, for example, that variations of the detected pressure is kept as small as possible. Consequently, the liquid can be ejected in fixed amount as intended.
Further, by mechanically opening the ejection orifice of the ejection valve in timed relationship with an increase of the force pressurizing the liquid in the liquid reservoir, the liquid ejection can be started without a time lag. At the end of the ejection, by removing the added increase of the pressurizing force and mechanically closing the ejection orifice of the ejection valve, one cycle of the liquid ejection in fixed amount can be ended with positive shutting-off of the liquid without a risk of liquid leakage.
After one cycle of the liquid ejection in fixed amount has been thus ended, the liquid pressure in the flow passage is controlled to be kept at the predetermined specific value depending on the detected liquid pressure in a similar way as described above.
With the apparatus of the present invention, in response to a pressure signal and a pressurizing time signal both supplied to the pressurizing means, the liquid in the liquid reservoir is pressurized for a time corresponding to the pressurizing time signal so that the liquid is held under a pressure corresponding to the pressure signal. Further, the ejection valve is opened in timed relationship with the operation of the pressurizing means, causing the liquid to be ejected through the ejection orifice. As a result, the ejection of the liquid can be started without a time lag. At the time when the time during which the liquid is pressurized by the pressurizing means reaches a predetermined time and the amount of the ejected liquid reaches a predetermined amount, the ejection valve is mechanically closed in timed relationship with the stop operation of the pressurizing means. The ejection orifice of the ejection valve is thereby physically closed. Therefore, the liquid is positively shut off and an accidental leakage of the liquid after the closing of the ejection orifice can be perfectly prevented. After one cycle of the liquid ejection in fixed amount has been ended, the liquid pressure near the ejection orifice is detected by the pressure sensor, and a detected pressure signal at that time is inputted to the control means. In accordance with the input signal, the control means controls the pressurizing means to raise or lower the liquid pressure so that the residual liquid pressure near the ejection orifice becomes the predetermined specific value. It is a matter of course that if the detected liquid pressure coincides with the predetermined specific value, the pressurizing means requires not to be operated again. By always keeping the liquid pressure near the ejection orifice and hence the pressure in the liquid flow passage at the constant values after the end of the ejection as described above, variations of the flow passage condition are eliminated. At the time of starting the next cycle of the liquid ejection in fixed amount, the force, time, etc. for pressurizing the liquid can be determined with no need of taking into account indefinite factors. In addition, the liquid can be ejected in fixed amount with high precision.
When one cycle of liquid ejection is continued for a relatively long time as experienced, for example, when the liquid is coated in the linear form, it is preferable that the pressure detection by the pressure sensor is also performed during the ejection and the liquid pressurizing force applied from the pressurizing means is controlled in accordance with the detected result.
In the apparatus of the present invention, preferably, the ejection valve comprises a needle valve. Since the size of a needle can be made in itself sufficiently small, the needle can be smoothly and quickly displaced to open and close by a relatively small driving force even under a high pressure on the order of, for example, 100 to 200 kgf/cm2. It is therefore possible to shut off the liquid more positively at the end of the ejection, and to eliminate a time lag more effectively at the start of the ejection. In addition, since the required driving force is relatively small, the overall size of the ejection valve can be reduced.
More preferably, the needle valve is provided with a liquid pressure compensating piston. With this feature, the apparatus can operate so as to compensate pressure variations in the liquid passage, particularly at and near the ejection orifice, more easily, quickly and precisely in combination with back and forth movement of the liquid pressure compensating piston. One example of the combined operation is as follows. When the needle valve is opened, the volume occupied by the needle in an area near the ejection orifice is reduced. Conversely, when the needle valve is closed, the volume occupied by the needle in the area near the ejection orifice is increased. In the former case, a drop of the liquid pressure near the ejection orifice can be prevented by moving forth the liquid pressure compensating piston. In the latter case, a rise of the liquid pressure near the ejection orifice can be prevented by moving back the liquid pressure compensating piston. Accordingly, the liquid pressure compensating piston can be employed in addition to or in place of the pressurizing means for the purpose of controlling the residual liquid pressure after the end of the ejection to the predetermined specific value.
Further, when an ejection nozzle requires to be moved relative to a workpiece in the apparatus of the present invention, the ejection nozzle is preferably mounted to a manipulator which is based on the Cartesian coordinate system and enables the ejection nozzle to be displaced in three dimensional directions. More preferably, the manipulator is controlled in synchronous relation to control of the pressurizing means and control of the ejection valve.
As described above, the fixed-amount-of-liquid ejecting apparatus according to the present invention is also realized as a pneumatic type apparatus. The pneumatic type apparatus will be described below. The pressurizing means is constituted by an air cylinder for moving forth and back a plunger which is inserted in the liquid reservoir, and the air cylinder is formed to have a bore diameter greater than the inner diameter of the liquid reservoir.
With the pneumatic type apparatus, a solenoid selector valve is operated in accordance with a signal supplied from the control means, and air pressurized under a predetermined pressure is introduced tot he air cylinder, which may be of the double-acting type, thereby pressurizing the liquid in the liquid reservoir with a plunger. Further, the ejection valve is opened in timed relationship with the above operation of the pressurizing means. As a result, the liquid can be ejected through the ejection orifice under a pressure corresponding to the pressure supplied to the air cylinder without a noticeable time lag.
On the other hand, at the time when the amount of the ejected liquid that is determined depending the pressure supplied to the air cylinder, the ejection time, etc. reaches a predetermined amount, the supply of the pressurized air to the air cylinder is stopped and at the same time the ejection valve is closed under control of the control means. Accordingly, the liquid ejection can also be stopped without a noticeable time lag, and therefore the liquid can be ejected in fixed amount with good precision.
In addition, since the liquid ejection is stopped upon the ejection valve being mechanically closed, the liquid can be positively shut off and a leakage of the liquid after the closing of the ejection orifice can be very effectively prevented.
In order to improve the efficiency of ejection work by repeating the above-describe liquid ejection in fixed amount with cycles of a short tact time, it is required to raise a force imposed by the plunger for pressurizing the liquid and to increase the amount of liquid ejected per unit time. However, because the line air pressure in a general factory is relatively low, i.e., on the order of 5 to 7 kgf/cm2, the liquid pressure can not be raised as intended if the line air pressure is just supplied to the air cylinder as it is. Accordingly, there has been a limit in the efficiency of ejection work. In the pneumatic type apparatus, therefore, the bore diameter of the air cylinder is set sufficiently greater than the inner diameter of the liquid reservoir so that the plunger can provide a sufficient level of pressing force even with a relatively low pressure supplied to the air cylinder. As a result, the liquid pressure can be raised to a desired level and the tact time for ejection of the liquid in fixed amount can be shortened.
In the above case, regulation of the liquid pressure, i.e., regulation of the pressure supplied to the air cylinder in terms of direct control target, can be performed by a pressure reducing valve disposed in a pneumatic line.
The pneumatic type apparatus preferably comprises a pressure sensor provided near the ejection orifice of the ejection valve and detecting a liquid pressure, and pressure regulating means for regulating the pressure supplied to the air cylinder in accordance with a signal from the pressure sensor. The detected signal from the pressure sensor is inputted to the control means, and the control means output a pressure regulation signal to the pressure regulating means which preferably comprises an electro-pneumatic regulator, thereby operating the pressure regulating means. As a result, the pressure supplied to the air cylinder can be automatically regulated as required, and pressure variations during the liquid ejection can be automatically compensated in a prompt and smooth manner.
Also in the pneumatic type apparatus, preferably, the ejection valve comprises a needle valve.
Since the size of a needle can be made in itself sufficiently small, the needle can be smoothly and quickly displaced to open and close by a relatively small driving force even under a high liquid pressure on the order of, for example, 100 to 200 kgf/cm2, without being hardly affected by the liquid pressure. It is therefore possible to shut off the liquid more positively at the end of the ejection, and to eliminate a time lag more effectively at the start and end of the ejection.
In addition, since the required driving force is relatively small, the overall size of the ejection valve can be reduced.
More preferably, the needle valve is provided with a liquid pressure compensating piston.
With this feature, the apparatus can operate so as to compensate pressure variations in the liquid passage, particularly at and near the ejection orifice, more easily, quickly and precisely in combination with back and forth movement of the liquid pressure compensating piston. One example of the combined operation is as follows. When the needle valve is opened, the volume occupied by the needle in an area near the ejection orifice is reduced. Conversely, when the needle valve is closed, the volume occupied by the needle in the area near the ejection orifice is increased. In the former case, a drop of the liquid pressure near the ejection orifice can be prevented by moving forth the liquid pressure compensating piston. In the latter case, a rise of the liquid pressure near the ejection orifice can be prevented by moving back the liquid pressure compensating piston.
Accordingly, the liquid pressure compensating piston can be employed in addition to or in place of the pressurizing means for the purpose of controlling the residual liquid pressure after the end of the ejection to the predetermined specific value.
More preferably, the liquid flow passage extended between the liquid reservoir and the ejection valve has a rising portion which extends upwardly while penetrating the plunger.
When the plunger is initially moved into the liquid reservoir, air is enclosed between a liquid surface in the liquid reservoir and the plunger which is preferably held in airtight contact with an inner surface of the liquid reservoir. However, where the liquid flow passage has the rising portion which extends upwardly while penetrating the plunger, the air enclosed above the liquid surface in the liquid reservoir is purged out of the liquid reservoir through the rising portion upon the plunger being pushed into the liquid reservoir prior to starting the liquid ejection in fixed amount. It is therefore possible to sufficiently eliminate an adverse effect of compressive property of the enclosed air upon a variation of the liquid pressure before entering the operation of ejecting the liquid in fixed amount.
To sum up, the present invention having the above-described construction operates as follows.
(1) From a method point of view, the method of the present invention comprises the step of applying a pressure to the liquid beforehand prior to starting ejection of the liquid and/or holding a pressure near an ejection orifice after the end of liquid ejection at a predetermined specific value, and from an apparatus point of view, the ejection valve includes the means for mechanically opening and closing the ejection orifice of the ejection valve. Therefore, when ejecting the liquid in relatively small fixed amount, for example, the pressure in the flow passage after the end of the ejection, particularly the pressure near the ejection orifice, is controlled to be kept at the predetermined specific value, whereby the subsequent ejection of the liquid can be always performed under the constant flow passage condition. Accordingly, by properly setting the force, time, etc. for pressurizing the liquid in the liquid reservoir, the ejection of the liquid in an amount corresponding to the set values can be repeatedly reproduced with high reliability.
The causes giving rise to a delay in ejection of the liquid reside in that it takes a time to raise the liquid pressure to a desired level, and that energy to be utilized for the ejection is consumed by deformations under pressure. Therefore, the above features of the present invention provide such advantages that pressuring the liquid prior to starting the ejection enables a desired force to act upon the liquid in a short time, and that developing deformations under pressure beforehand is effective suppressing further deformations during the ejection. As a result, energy supplied for making the liquid flow can be effectively utilized. Preferably, the pre-pressurization is carried out by applying a force equivalent to the pressure applied during the ejection, and the ejection is ended while maintaining the force equivalent to the pressure applied during the ejection.
(2) By controlling the liquid temperature to be held constant, it is possible to suppress one, more exactly, primary one of factors which cause a change of the liquid viscosity, and to eject the liquid in fixed amount with stability.
(3) By controlling the pressure of the liquid stored in the liquid reservoir, a thrust exceeding the pipe resistance developed in a nozzle is applied to act upon the liquid, and therefore an ejection rate of the liquid can be controlled to be held constant.
Because the liquid is ejected after passing a nozzle optimum for a shape to be drawn by the applied liquid, the liquid is subjected to some pipe resistance developed in the nozzle. However, controlling the pressure of the liquid stored in the liquid reservoir can produce a thrust exceeding the pipe resistance. Such control is particularly effective in the case of ejecting a highly viscous fluid in which the liquid is subjected to a very large pipe resistance. No matter how large resistance is developed, a thrust exceeding the resistance can be produced so as to act upon the liquid, and the ejection rate of the liquid can be controlled to be held constant.
(4) Control of the pressure of the liquid stored in the liquid reservoir is performed by controlling, concretely constant or variable, a rate at which the liquid stored in the liquid reservoir reduces. With the control, the ejection rate of the liquid can be held constant or as desired from the start of the ejection to the end of the ejection.
Controlling, concretely constant or variable, a rate at which the liquid stored in the liquid reservoir reduces implies that the concept of time is added to the prior art wherein time is not taken into consideration if a desired volume of the liquid is obtained, and that the volume of the ejected liquid is gradually increased in units of predetermined amount even during the process for achieving the desired volume of the liquid. As a result, the liquid can be applied regardless of viscosity of the liquid. In addition, even in the case of ejecting a highly viscous liquid that has not been preferred in practical use up to now, an adverse effect caused by resiliency of the push member and the liquid reservoir can be effectively eliminated, thus allowing these components to be employed so that the liquid can be easily applied in a desired shape with stability. Further, the ejection work can be performed at a high speed because of no need of returning the liquid pressure to the atmospheric pressure.
(5) The push member disposed to push the liquid stored in the liquid reservoir in a precise and fluid-tight manner controls the amount of the ejected liquid in accordance with a distance through which the push member moves, and also controls the flow speed of the ejected liquid in accordance with a speed at which the push member moves. Further, the liquid pressure is controlled such that the liquid is pressurized to a certain level prior to starting the ejection, and the ejection is ended under the liquid pressure higher than the atmospheric pressure, preferably when the liquid pressure is at the same pressurized level as before the start of the ejection. Therefore, adverse effects due to changes of viscosity can be eliminated, and the rate at which the liquid is ejected through the nozzle end can be controlled to be always held constant. Further, it is possible to overcome a difficulty that has been especially experienced in the prior art, i.e., precise application of the liquid so as to provide a proper form in starting and ending portions of the applied liquid line. The effect of the above feature is more effect particularly when the liquid is applied in a linear form, and a linear shape in starting and ending portions of the applied liquid line, which has been unstable in the prior art, can be very easily controlled. When the liquid should be applied in a uniform linear line, for example, the applied liquid line can be formed with a uniform width from the start point to the end point of the line without narrowing and fatting.
(6) Since the bore diameter of the air cylinder for pressing the push member is set sufficiently greater than the inner diameter of the liquid reservoir, the plunger can provide a sufficient level of pressing force even with a relatively low pressure supplied to the air cylinder. As a result, the liquid pressure can be raised to a desired level and the tact time for ejection of the liquid in fixed amount can be shortened.
(7) A motor is employed as a power source for pressing the push member, and energy generated by the motor is much greater than that required for making the liquid flow. Therefore, the moving speed of the push member can be kept constant.
(8) In addition, the present invention intends to prevent bubbles from being entrapped particularly when the liquid is filled in a syringe. The present invention also intends to eliminate the necessity of monitoring the filling process and adjusting the filling speed by a worker for the purpose of avoiding entrapment of bubbles. The present invention is featured by a fully automatic filling process. The present invention concerns with a reliable technique for ejecting a liquid in fixed amount.
(9) In particular, the present invention is applicable to any work steps for filling a liquid having a medium or higher level of viscosity. The liquid reservoir is preferably of the type that the liquid filled therein is employed by being pushed out of the reservoir end.
The liquid reservoir filled with the liquid constitutes a liquid reservoir of an apparatus comprising the liquid reservoir, liquid pressurizing means for pressurizing the liquid stored in the liquid reservoir under a pressure depending on the viscosity of the liquid, and an ejection valve communicating with the liquid reservoir, thereby ejecting the liquid in fixed amount from the liquid reservoir through the ejection valve.
With the present invention having the above-described construction, the following advantages are expected.
(1) A method and apparatus can be provided which can eject or apply a very small amount of liquid in a desired form at a high speed and precisely without depending on viscosity of the liquid. Particularly, even when employing a highly viscous liquid or applying a liquid at a high speed, a shape of the applied liquid line can be very easily controlled in starting and ending portions of the applied liquid line. For example, when the liquid should be applied in a linear uniform shape, the applied liquid line can be formed with a uniform width from the start point to the end point of the line without narrowing and fatting.
(2) The liquid can be more positively shut off at the time of stopping the liquid ejection without a risk of breaking fillers, and a leakage of the liquid can be securely avoided.
(3) A liquid ejecting or applying method and apparatus can be provided which enables an applied liquid to be drawn in a uniform line without taking a time until a flow speed of the liquid reaches a certain value.
(4) When filling a liquid in the liquid reservoir, particularly in a syringe, the liquid can be filled without entrapping bubbles while realizing a fully automated manner.